MadGraphControl Fix, 21.6.43-patches branch (2020.11.02.)

Taught MadGraphControl's lhapdf-config script to remember which version of Boost to use. So that the script would would with non-CVMFS-based installations as well.

This is to fix the issue discussed in AGENE-1925.

This is a twin of !37818 (merged).

added 21.6 bugfix labels

merged

mentioned in commit 101318aa